With the advent of alternative fuels like alcohol, biodiesel and mixed fuels like, E85 (85% ethanol and 15% gasoline) and M85 (85% methanol and 15% gasoline) there is a desire to use them in motor vehicles, motorboats and other motorized machines like trucks, tractors, lawnmowers, etc. that were not previously designed to operate on such alternative fuels. With gasoline and diesel prices rising to record levels, alternate fuels are starting to make inroads with average American consumers. Also atmospheric pollution generated by exhaust emissions from conventional gasoline or diesel powered internal combustion engines is a well-documented problem. Not only do alternate fuels burn cleaner with less harmful air pollution, the fuels can be made here at home in the United States from a variety of agricultural feedstock thereby reducing the consumption of foreign oil.
A motor vehicle capable of burning mixtures of gasoline and alcohol is commonly called a Flexible Fuel Vehicle (FFV). Today's commercially available FFVs typically burn any mixture from 85% ethanol or methanol to 100% gasoline. A diesel FFV can burn any mixture of diesel and biodiesel and ethanol is also known to be mixed with diesel. The operation of a FFV is a well-known art. They all use a single fuel reservoir or tank and the fuel to alcohol ratio in the tank is often measured directly using a fuel composition sensor or via exhaust feedback from an exhaust gas sensor. The information from either type of sensor is read by the engine's control module and the result is used to control the quantity of fuel being fed into the engine and thereby the engine's air to fuel ratio.
Controlling the quantity of fuel is necessary because alcohol fuels like ethanol and methanol have less energy per unit volume than gasoline or diesel and require a much smaller air to fuel ratio when burned in an internal combustion engine. While gasoline has an ideal air to fuel ratio of about 14 to 1, pure ethanol has a ratio of about 9 to 1. A fuel injection system in a FFV instantly compensates to maintain stoichiometric over wide percentage changes in the fuel mix. Therefore the principal advantage of a FFV is its ability to arbitrarily be refueled both with pure fuels and mixed fuels.
In the late 1990s, automotive manufactures began producing FFVs. Even though FFVs today make up a small percentage of vehicle sales there is a growing need for FFVs. The need is being driven mostly by the rise in crude oil prices, the desire for reduced exhaust emissions, and the need to reduce the import of foreign oil. Since there are only a few vehicle models made as FFVs, there is growing need to modify previously manufactured vehicles like classic cars, trucks and SUVs to make them fuel flexible. Classic cars and modern sports cars with high compression engines typically get poor gas mileage, have high levels of emissions and will additionally benefit from the high octane of alcohol based alternate fuels. Therefore there is a need to convert conventional gasoline and diesel burning vehicles already being used on the highways today into Flexible Fuel Vehicles.
Since these vehicles were not manufactured to operate on alternate fuels, the addition of a flexible fuel engine control system is needed. Although the parent patent application disclosed several methods and corresponding apparatus for retrofitting engines that originally were manufactured with either carburetors or electronic fuel injection, the patent application did not address the optimization needed in order to obtain peak performance of the converted engine. The flex fuel engine control system added to the engine must be optimized to ensure the engine operates at its highest efficiency regardless of the mixture of fuel used. This is important because the octane ratings and energy released by the same volume of the alternate vs. conventional fuels can be quite different.
When converting an OEM type engine that has an OEM type carburetor, most often carburetors have to be rebuilt as their seals and gaskets are either worn out or are not compatible with an alternate fuel like alcohol. Even after a rebuild of the gaskets and seals, the throttle shafts of the carburetor may be worn enough to cause the carburetor to leak air at the throttle plates. In some cases this leakage is enough to cause drive-ability issues at idle and low speeds as the leak upsets the carburetors ability to control the air to fuel mixtures for proper combustion. In other cases where the leak is only minor, just a change in emission levels is noticeable.
When converting an OEM type engine with a carburetor, it is necessary to supplement the carburetor's flow with a wide dynamic range of fuel flow. Alcohol and gasoline fuels burn with very different air to fuel ratios. Because the amount of alcohol in OEM fuel tank mixtures can vary in ratio from 0 to 100%, the amount of fuel added by the flex fuel control system may be quite small or very large at any given time. This wide dynamic range of fuel delivery often exceeds the capability of modern day fuel injectors and thus may require additional injectors in order to provide the supplemental fuel flow for Flex Fuel operation.